1. Field of the Invention
The invention relates generally to deepwater pipeline laying and more particularly to an abandonment and recovery (A&R) system and method, and an A&R cable connector, in particular for deep water applications.
2. Background of the Related Art
The J-lay method is commonly used for deepwater pipelaying. With this method each portion of the pipeline to be laid is erected to a vertical position, welded to the main pipe line and lowered directly into the water with a single bend, giving the pipeline which is being laid the form of a “J”.
Also the S-lay technique is becoming more and more popular for deepwater and ultra-deepwater pipelaying. With this method each portion of the pipeline to be connected is welded to the main pipeline and moved in a horizontal position over the stinger into the water, with a double bend giving the pipeline which is being laid the form of an “S”. The S-lay technique has the advantage that it allows higher lay rates.
When a load, such as a pipeline or a sub-sea structure must be abandoned from a vessel, a typical method consists of welding an abandonment and recovery (A&R) head with a lifting eye to the end of the pipeline or sub-sea structure. A coupling shackle connected to a cable coupled to a winch on the vessel is connected to the lifting eye of the A&R head and the pipeline or sub-sea structure is lowered to the seabed.
J-lay and S-lay for deepwater applications entail not only the use of heavy tension equipment, but also require extra winch capacity and in particular cables with a very high tensile strength to support the high load resulting from the long length of pipeline, which initially extends from the vessel to the seabed. However, the diameter of the cable is typically limited, so that choosing to use a thicker cable at these lengths cannot solve the extra capacity needed. Also winches capable of handling loads of 500 T or more are not common and expensive.
Another problem of the existing A&R systems and methods relates to the control of the movement of the cables, and especially the rotation thereof during abandonment or recovery.
International patent application WO 01/48410 discloses a method of abandoning a pipeline being laid by a vessel having an A&R system, wherein a sealine is initially held by a pipe laying and tensioning arrangement. The method includes a step of reducing the tension at sea level by connecting one or more light buoyant elongate members to the end of the pipeline. This method has the disadvantage that special buoyant elongate members are needed and that the connection thereof may be time consuming. Moreover this technique is not well suited for S-lay because the buoyant elongate members have to pass over the stinger.
Hence, it would be desirable to provide an A&R system and A&R cable connector that solves at least partly the problems discussed above.